Disk drive motor, and method of manufacturing its rotor

Abstract

A motor rotor 10 is formed as follows: First, in a first forging step, a hum manufacturing primary block 6A is formed. Next, a second forging step B is effected to form the primary blank 6A into a secondary blank 6B. In this step, a forging die is used to secure an annular yoke 34 to the inner cylindrical surface 61a of a hub cylindrical portion 61 by punching, in such a manner that both whole edges of the annular yoke are sealingly closed thereby. In the second forging step B, by drawing the inner cylindrical surface 34a of the annular yoke, its circularity is improved. The annular yoke can be secured to the hub cylindrical portion with use of an adhesive agent. Moreover, the annular yoke can be fixed in such a manner that it is accurately coaxial with the hub cylindrical portion. In addition, the gap between the annular yoke and the hub cylindrical portion can be eliminated.

What is claimed is: 
     
       1. A method of manufacturing a motor rotor in which a yoke having an annular shape is fitted in a cylindrical portion of a hub, and a drive magnet is fitted in the yoke along an inner cylindrical surface of the yoke, comprising: a first forging process comprising processing a die forging for a non-magnetic metal material to form a hub manufacturing primary blank which has the cylindrical portion, and first and second punching portions which are annular and with which the yoke can be fixed by punching; and   a second forging process comprising processing a die forging for the primary blank to form a hub manufacturing secondary blank which is substantially similar to a final product,   wherein, in said second forging process, with the yoke inserted into the cylindrical portion, the first and second punching portions are crushed with a forging die to fix the yoke by punching in such a manner that both whole edges of the yoke are sealingly closed by the first and second punching portions, and   wherein said second forging process comprises increasing circularity of the yoke by forcibly pushing a part of the forging die in the yoke along the inner cylindrical surface of the yoke.   
     
     
       2. A method as claimed in claim 1, wherein, after said second forging process, the drive magnet is fitted in the yoke along the inner cylindrical surface of the yoke. 
     
     
       3. A method of manufacturing a motor rotor in which a yoke having an annular shape is fitted in a cylindrical portion of a hub, and a drive magnet is fitted in the yoke along an inner cylindrical surface of the yoke, comprising: a first forging process comprising processing a die forging for a non-magnetic metal material to form a hub manufacturing primary blank which has the cylindrical portion, and first and second punching portions which are annular and with which the yoke can be fixed by punching; and   a second forging process comprising processing a die forging for the primary blank to form a hub manufacturing secondary blank which is substantially similar to a final product,   wherein, in said second forging process, with the yoke inserted into the cylindrical portion, the first and second punching portions are crushed with a forging die to fix the yoke by punching in such a manner that both whole edges of the yoke are sealingly closed by the first and second punching portions, and   wherein, after said second forging process, finishing is performed by machining the secondary blank into the final product, and during the finishing, the inner cylindrical surface of the yoke is employed as a finishing reference surface.   
     
     
       4. A method as claimed in claim 3, wherein, after the finishing is performed, the drive magnet is fitted in the yoke along the inner cylindrical surface of the yoke. 
     
     
       5. A method as claimed in claim 3, further comprising holding the inner cylindrical surface of the yoke with a chuck during said machining.